UNO clone, LED is telling me something but what?

When I first power the UNO, the LED at D13 starts flashing a sequence before it runs the sketch (like the classic blink sketch) I have not seen this on the genuine UNO so I am wondering if it's telling me something.

The clone uses CH340G USB to serial chip because other chips (FTDI and AVR) are hard to hand solder. 16u2 for example, the commonly used chip package is not meant to be hand soldered, modifying the design to use larger TQFP would require rearranging a lot of parts. Using FTDI chip is also hard, with pin spacing at .025" while CH340G is .05 and slightly easier for me. (that said, anyone willing to donate me a reflow oven? So I could build smaller parts?)

On power on, it flashes I think 6 times, goes off, flashes 4 times, goes off, flashes 4 times, goes off, flashes 4 times, goes off, flashes 4 times, goes off, flashes 4 times, goes off, then run whatever uploaded code.

I used regular UNO bootloader when I programmed the chip for the new UNO clones I made.

Looks like forum doesn't handle Imgur MP4 or GIFV file as images, here's the direct link

Not 100% sure; the sequence is different from what I remember for the Uno. But it's probably indicating that the boot loader is active. No Uno at hand to verify the usual behaviour.

The Uno boot loader has evolved over time; maybe the sequence that you see is the result of a different version of the boot loader.

Very weird. AFAIK, there is no uno-like boot loader that does this.

Where are you getting CH340G to hand solder onto boards?

Pick up a toaster oven at a yard sale. If you can find one with 4 heating elements, that's the best, 1500W will support reflow profiles very well. I have an ancient Sears-Kenmore myself.
Then get a multimeter with a thermal probe, for example
MN35 Extech Handheld 600 V 3.5 Digit 600 V Multimeter New?
I have a similar Extech meter, 2 in fact, one is usually with the oven, and a 2nd up in the workshop. Or somewhere, they move around the house.

Put board in the oven, with probe tip near it.
Heat to 150C, wait 90 seconds, heat to 190C, wait 90 seconds, let it cool. I just time it on my phone.
Works pretty well for me. If your oven has a window in front, then visually watching for when the paste turns from grey to melted can help you calibrate the times needed.

Most parts have a never exceed temperature (like 205C), check the datasheets on what you are using.

Your solder paste may need a slightly different profile.

So... this is your own design? And that blindingly bright green LED is "power"? And this is the behavior you see when plugging the board into a computer?

Does it do the same thing if you plug it into something like a powerbank?

A couple possible explanations:

  • errors in the auto-reset circuitry.
  • multiple resets due to host-side software. Say, one when powered on, one when the USB port is enumerated as a serial port, another when some host-side SW sees the serial port and opens it, and another if the host-side SW closes the port again. (assuming the host SW is smart enough to recognize the Uno as "not my device", while the CH340 looks like "generic serial port; could be mine!"

Exactly which bootloader did you use? One problem with "scenario 2" is that I don't think that recent optiboots will start the bootloader on powerup... ("Adafruit fast start mod")

Where are you getting CH340G to hand solder onto boards?

eBay. Most of my favorite sources like Mouser and Digikey doesn't carry chips only, they have fully assembled serial board with CH340g There's also Aliexpress but I've heard the chargeback can be a pain in the butt if the seller screws up. eBay almost always side with the buyer if there's problem with the chips.

So far I haven't had any chip issue, always worked between computer and my custom Arduino board. This is the seller I got mine from: 174405414394 (ebay search the number), no tracking but at about a dollar a chip or less, it's plenty cheap.

CH340c is nearly identical to g version except c does not require external clock, a plus if board space is at premium. Right now the cost saving by leaving a crystal and 2 capacitors is not enough for me to switch from g version.